1. Field of the Invention
The invention relates to paving machines and, more particularly, relates to pavers of the type having a distributing auger, a screed, and a hopper for storing hot mix asphalt (HMA) or other paving materials and for delivering the paving materials to the distributing auger and screed.
2. Discussion of the Related Art
Floating screed-type paving machines are well known for the laying of HMA on roadways. Such machines typically include a self-propelled tractor-like vehicle having an engine for propulsion and for material distributing functions; a hopper provided at the front of the machine; a distributing auger mechanism provided at the rear of the machine; and a heated vibratory screed provided behind the distributing auger. The hopper, typically having a capacity of about 12 tons, is relatively low and extends all the way to the front of the paving machine so as to be capable of receiving HMA directly from a truck positioned in front of and pushed by the paving machine as the paving machine travels along the roadway. Hoppers of this type are incapable of feeding HMA by gravity to the distributing auger mechanism and thus require an internal conveyor mechanism to convey materials from the front of the hopper to a rear discharge opening located adjacent the distributing auger mechanism. This conveyor mechanism typically takes the form of a pair of parallel drag slat conveyors extending longitudinally of the hopper and communicating with independently operable feeder gate mechanisms located at the discharge opening.
Paving machines with hoppers having internal conveyors, though operationally adequate, exhibit several drawbacks and disadvantages. For instance, the drag slat conveyors typically used to convey aggregate in the hopper towards the rear discharge opening are relatively expensive to install and maintain and, indeed, are typically the most expensive part of the paving machine to maintain. It is also relatively difficult to maintain a uniform discharge of materials from the hopper using such conveyors, particularly when the hopper is nearly empty during which time less or even no materials are delivered to the discharge opening between the times at which successive flights of the conveyors reach the openings. Substantial hand work is required at the end of the mat to compensate for this deficiency and to deliver to the discharge openings any materials which are inaccessible by the conveyors. The problem of uneven feed of materials from the hopper can be partially alleviated by permitting the speeds of the parallel drag slat conveyors to be independently controlled by the operator(s) as disclosed in U.S. Pat. No. 3,453,939 to Pollitz et al. Such a control system, however, necessarily increases further the cost and complexity of the paving machine and also places additional burdens on the operators.
Moreover, a relatively large engine is required because 1) the paving machine must push the truck along the roadway as the truck delivers materials to the hopper, and 2) significant power is required to operate the conveyors in the hopper.